Optimizing the Aromatic Product Distribution from Catalytic Fast Pyrolysis of Biomass Using Hydrothermally Synthesized Ga-MFI Zeolites

Jian Li,Xiangyu Li,Xinning Lu,Yujue Wang,Derun Hua

doi:10.3390/catal9100854

Abstract

A series of gallium-containing MFI (Ga-MFI) zeolites with varying Ga2O3/Al2O3 ratios were synthesized using hydrothermal synthesis and tested as catalyst in catalytic fast pyrolysis (CFP) of beech wood for aromatic production. The results show that the incorporation of Ga slightly reduced the effective pore size of Ga-MFI zeolites compared to conventional HZSM-5 zeolites. Therefore, the Ga-MFI zeolites increased the aromatic selectivity for smaller aromatics such as benzene, toluene, and p-xylene and decreased the aromatic selectivity for bulkier ones such as m-xylene, o-xylene, and polyaromatics in CFP of beech wood relative to HSZM-5. In particular, the yield and selectivity of p-xylene, the most desired product from CFP of biomass, increased considerably from 1.64 C% and 33.3% for conventional HZSM-5 to 2.98–3.34 C% and 72.1–79.6% for the synthesized Ga-MFI zeolites. These results suggest that slightly reducing the pore size of MFI zeolite by Ga incorporation has a beneficial effect on optimizing the aromatic selectivity toward more valuable monoaromatic products, especially p-xylene, during CFP of biomass.

Highlights

Aromatic hydrocarbons derived from petroleum are widely used to manufacture a wide range of downstream products, such as synthetic plastic, medicine, and gasoline additives
The high aromatic yields of HZSM-5 can be primarily attributed to its moderate acid sites and suitable micropore size, Catalysts 2019, 9, 854; doi:10.3390/catal9100854
ZSM-5 zeolite exhibits low selectivity (~30–53%) for p-xylene, which is the most desirable aromatic product from catalytic fast pyrolysis (CFP) because of its high value and importance for polyethylene terephthalate production [17]. These results indicate that the product distribution from CFP of biomass with the conventional ZSM-5 zeolite still has vast potential for further improvement

Summary

Introduction

Aromatic hydrocarbons derived from petroleum are widely used to manufacture a wide range of downstream products, such as synthetic plastic, medicine, and gasoline additives. Lignocellulosic biomass is the most abundant and sustainable carbon resource on the earth [3] It has been considered attractive feedstock for producing valuable aromatic hydrocarbons, such as benzene, toluene, and xylenes (BTXs), which are the building-blocks of the petrochemical industry to produce numerous petrochemical intermediates and commercial products [1,4,5]. Catalytic fast pyrolysis (CFP) of biomass with zeolite catalysts has attracted growing attention because it can directly convert lignocellulosic biomass to valuable aromatic hydrocarbons, especially BTXs. During CFP of biomass, the framework and acidity of zeolite catalysts play an important role in the distribution of final products [6,7,8,9]. The high aromatic yields of HZSM-5 can be primarily attributed to its moderate acid sites and suitable micropore size, Catalysts 2019, 9, 854; doi:10.3390/catal9100854 www.mdpi.com/journal/catalysts

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Results

Conclusion